docs: def calc_sasa(dssp_df):
      """
      Calculation of SASA utilizing the DSSP program.
  
      DSSP must be installed for biopython to properly call it.
      Install using apt-get on Ubuntu
      or from: http://swift.cmbi.ru.nl/gv/dssp/
  
      Input: PDB or CIF structure file
      Output: SASA (integer) of structure
      """
  
      infodict = {'ssb_sasa': dssp_df.exposure_asa.sum(),
                  'ssb_mean_rel_exposed': dssp_df.exposure_rsa.mean(),
                  'ssb_size': len(dssp_df)}
  
      return infodict